Popping at the start of a recording...

So I was recording this song. (I use Cubase LE and a Firebox) and I tried doing a few things. First, I tried playing this chorus riff once through, and I resized it so that it was the perfect amount of beats so I could simply copy and paste. So I pasted it 4 times in a row, and it flowed really good. The only slight problem is, is as the next copied one starts theres a little tiny pop. How do you prevent that from occuring? And how can you get rid of it (without any huge tedious work?) This also happened when I tried cutting a piece out of a riff (I have good rythm and I was using a metronome so it came out good). I cut that piece out, and replaced it with something else and it sounded fine, but again, the pops were in the beginning and end of that middle riff. Any suggestions is appreciated!